( 202 ) 



In the point o coexists a vapour with tlie two solid phases A and 

 AB and the point U\ denotes the composition and the pressure of 

 the A-apour phase w^hich can coexist at the entectic temperature 

 with a liquid E' and two solid phases AB and B. 



In the second 2>cU-section the cur\es /■,/, ^/j ^, ^^r^ e' and //j /' represent 

 vapours coexisting with solid phases ; the lines m c and m' c' denote 

 the liquids coexisting with the vapours e I and e' I', while the lines 

 ms, cf, c^f' and m' s' represent liquids coexisting with solid phases. 



What change this section is subjected to with rise of temperature 

 is so eas}^ to follow from the diagram, that it does not call for a 

 discussion. 



It maA' only be observed here that for the case that the combi- 

 nation reaches its critical point sooner than the components, we get 

 somewhat above this temperature a 7>.ï-section which consists of two 

 loops bs X and h\ y, in which the vapour branches have continuously 

 passed into the liquid branches, and an opening has been formed 

 between the two loops. This, however, does not complete the 'p-x- 

 section, for, solid phases may still occur by the side of liquids at 

 higher pressures, though above the critical temperature of A B and 

 the melting point of A and B, when viz. .4, B and AB melt with 

 increase of volume, as generally happens. Thus the lines k.^s^ g^f^, 

 g^ f\ and k' .^ s\ represent the liquids w^hich can coexist with a 

 solid phase at the same temperature. 



After this discussion of fig. 1, it is not necessary to give a fur- 

 ther explanation of figs. 2 and 3, which represent the second and 

 third case, as these figures do not present any essential differences 

 with fig. 1. 



3. It is more interesting to see what happens, when the combi- 

 nation A B dissociates somew^hat. In this case the total p-.r-section 

 is no longer to be considered as two separate p-.i'-figures joined, but 

 as one whole and we arrive therefore at the conclusion, which sounds 

 rather paradoxical, that the characteristic feature of a combination 

 becomes apparent only when the combination is somewhat decomposed 

 into its components. All the curves which meet at an angle in the 

 figs. 1, 2 and 3 at the place of the line for the combination, now 

 pass continuously into each other. This applies, therefore, not only 

 to the gasUnes, but also to the lines which bound the three phase 

 regions. 



With regard to the gradual transition of these three phase regions, 

 it may be observed, that it does not take place at the point where 

 the three phase region lines cut the line for A B, but always left 



